In the processing of materials containing metal values, two of the main extractive methods to be considered are pyrometallurgy and hydrometallurgy. In the former, metal-containing material such as ore, slag, scrap, etc., is heated with appropriate agents such as reducing agents, fluxing agents, sulfidizing agents, chloridizing agents and/or oxidizing agents, etc., usually to the melting or fusion point of the mixture. At this temperature there is generally a separation of metallic values from gangue or waste materials. The procedure then calls for separating the metallic values from slag or waste material at a temperature at which both are molten. The phase containing the metal values is then cast to some convenient shape for use or for further refining, whichever is appropriate for the particular system involved. The very high temperatures involved in this technique are achieved via electric furnaces, blast furnaces, reverberatory furnaces, etc. Temperatures required for metals such as copper, nickel, iron would generally range from about 1100.degree. C. to about 1650.degree. C. An advantage in this method is that recoveries of the metal values are typically quite high.
The hydrometallurgy approach differs substantially from pyrometallurgy in that, although the metal bearing material such as ore, slag, scrap, etc., may be heated with agents such as reducing agents, oxidizing agents, sulfidizing and chloridizing agents as part of the procedure, the temperatures involved are generally much lower than with the usual pyrometallurgical method. These temperatures typically may be about 260.degree. C. to about 1050.degree. C., temperatures generally well below the fusion point of the metal-containing material.
Following this step, the treated metal-containing material then is contacted with an appropriate aqueous solution for extracting metal values by dissolution. The metal is then removed from the solution by precipitation, solvent extraction, evaporation of solvent, etc. The metal-containing residue obtained is then handled appropriately to further refine the metal. Although conditions of temperature are generally much lower than in pyrometallurgy, it is frequently found that recovery of the metal values is also lower than in the pyrometallurgical method.
A particular case where this is true concerns the extraction of nickel and cobalt from lateritic nickel ores. The pyrometallurgical processes range from the use of an electric furnace for the direct smelting of ore to produce ferronickel through similar techniques involving the blast furnace in which an iron-nickel-sulfide matte is obtained. The extraction of nickel from the ore using this method is greater than 90%.
Of the several hydrometallurgy approaches used commercially for treating this type of ore, the practice on a limonite ore or a highly serpentinic ore, such as that at Nicaro, Cuba, involves roasting the ore in a multihearth furnace while a reducing gas, such as producer gas, passes countercurrent to the ore. Temperatures in this case range from about 900.degree. to about 1350.degree. F. Following the roasting step, the ore is cooled in the absence of air, mixed with an ammoniacal ammonium carbonate solution and vigorously agitated and aerated. This results in the dissolution of nickel and cobalt, separating them from the bulk of the ore. This solution then is treated with steam, driving off ammonia and precipitating nickel carbonate. This product then is treated further to obtain the appropriate form of nickel or use as such. In comparison to the pyrometallurgical process, however, nickel extractions using this method have only been of the order of 70 to 80%.
Several other hydrometallurgy methods involve the use of procedures which include a roasting step with chlorides or sulfates but in other than reducing atmospheres, and the roasted ore is leached with an appropriate solvent such as dilute sulfuric acid. Alternatively, in certain cases the ore can be leached directly, such as with sulfuric acid solution but this is practical only when the magnesia content of the ore is low.
The extraction of metal values from metal bearing sources may be improved when the reductive roast is effected in the presence of certain additives such as added hydrogen halide, added sulfur, added sulfur-containing compounds, or combinations of these additives.
As will hereinafter be shown it has now been discovered that when the extraction or leach of the metal bearing source after the reductive roast is effected using an ammoniacal ammonium chloride solution, the extraction of the desired metal such as nickel from the metal bearing source will be accomplished in such a manner so that higher percentages of the desired metal will be extracted from the source with accompanying economical advantages.
This invention relates to an improvement in a process for the obtention of metal values from metal bearing sources. More specifically, the invention is concerned with an improvement in a process for the recovery of metal values from a metal bearing source in which the leach or extraction of the metal from a source which has been subjected to a reductive roast is effected by utilizing an ammoniacal ammonium chloride solution.
While the reductive roast may be effected in the absence of any additives, the dydrometallurgical extraction of metal values has been found to be improved when the reductive roast of the metal bearing source is effected in the presence of additives comprising added hydrogen halide, added solid sulfur, added sulfur-containing compounds or combinations thereof. While the exact reasons for the improved results or the mechanism by which they are accomplished are not known, several explanations therefore may be offered, with the understanding that the applicant does not intend to be limited thereto. One explanation is that the additive may act to reduce or to facilitate reduction of the combined metal or to otherwise assist in liberating the metal, whereby it is readily extractable. Another explanation is that the combination of additives may act or facilitate such action to reduce the nickel in an iron-nickel alloy to thereby convert the nickel into a readily extractable form. Still another explanation is that the combination of additives may act to prevent recombination of the metal into a form in which it is less readily extractable.
It is recognized that different ores respond differently to different additives and that greater improvement in the recovery of metal values may be obtained with some ores when the roasting is conducted in contact with a mixture of added gaseous sulfur compound and added sulfur or in contact with added gaseous sulfur compound and added hydrogen halide or when the roasting is effected in contact with all three of these additives. Also, it is recognized that some added gaseous sulfur compounds will respond differently in this system than other added gaseous sulfur compounds. Accordingly, the specific added gaseous sulfur compound and the added sulfur and/or added hydrogen halide will be selected with reference to the particular ore to be processed.
As hereinbefore set forth, improved recovery of metal values is obtained when the roasting of the metal-containing material such as ore, slag, scrap, etc., is effected in contact with additives such as gaseous sulfur compounds, added solid sulfur, and/or added hydrogen halide, whereby the recovery of the metal value is effected in a considerably higher yield than heretofore obtained in the hydrometallurgical system.
The process of the present invention may be used for the recovery of metal values from ore, slag, scrap or other metal bearing source and is particularly applicable to the recovery of nickel from such sources. However, it is to be understood that the process may be used for the recovery of other metal values including, for example, cobalt, copper, manganese and other metals which are soluble in ammoniacal ammonium chloride solutions, but not necessarily with equivalent results. In the interest of brevity, the following discussion will be directed to the recovery of nickel, with the understanding that it may be applied to the recovery of other metals as hereinbefore set forth.
As another advantage to the present invention, the process may be conducted in conventional apparatus and may utilize much of the conventional steps of prior art processes. Accordingly, the ore such as a lateritic nickel ore or other metal bearing source is prepared in a manner suitable for the process, such as finely divided or comminuted particles in a conventional way. The particles may be within a size range of from about 8 mesh to about 500 mesh or smaller and preferably within a range of from about 48 mesh to about 200 mesh. The particles then preferably are dried in a conventional manner to lower the moisture content of from about the usual 25% to 50% down to about 8% or 10% or less. The drying generally is effected in a rotary kiln at conventional temperatures.
The added solid or gaseous sulfur compound will be used in a sufficient concentration for the purpose and any be within the range of from about 0.01% to about 10% and preferably from about 0.1% to about 5% by weight of the ore. Any suitable sulfur bearing compound may be used in the present invention. Preferred gaseous sulfur compounds comprise hydrogen sulfide, sulfur dioxide, sulfur trioxide, carbonyl sulfide, carbon monosulfide, carbon disulfide, etc. For ease of use, the sulfur compound can also be added in solid form prior to roasting. However, in another embodiment, it may be normally liquid and vaporized prior to use or allowed to vaporize under the conditions existing in the reducing zone. In another embodiment, the added sulfur compound is a hydrocarbyl sulfide including, for example, methyl mercaptan, ethyl mercaptan, propyl mercaptan, butyl mercaptan, pentyl mercaptan, hexyl mercaptan, etc., but generally containing not more than about 20 carbon atoms per molecule. The solid sulfur which may be used will be in solid forms including powder, flour, granules, pellets, etc., as molten or as otherwise liquefied sulfur, as sulfur vapors, or if so desired, sulfur can also be added as metal sulfides such as pyrite. Generally speaking, the sulfur is employed in a concentration of from about 0.01% to about 5% and preferably from about 0.15% to about 3% by weight of the ore. When the additive comprises a hydrogen halide, the hydrogen halide is used in a concentration of from about 0.01% to about 10% and preferably from about 0.1% to about 5% by weight of the ore. Any hydrogen halide gas or liquid may be used and preferably comprises hydrogen chloride or hydrogen bromide. It is also contemplated within the scope of this invention that hydrogen iodide or hydrogen fluoride may also be employed but not necessarily with equivalent results. In still another embodiment, a precursor of hydrogen halide may be used and may be selected from free halogen, chlorine, bromine, iodine, fluorine or other suitable compounds selected from boron halides, carbon halides, phosphorous halides, silicon halides, etc. In still another embodiment, the precursor may comprise a hydrocarbon halide which preferably contains not more than about 20 carbon atoms per molecule.
It is therefore an object of this invention to provide an improvement in a process for effecting the recovery of metal values from a metal bearing source by utilizing a certain basic compound as a leach agent.
In one aspect an embodiment of this invention resides in a hydrometallurgical process for the recovery of metal values from a metal bearing source containing a metal selected from the group consisting of nickel, copper, cobalt and manganese which comprises the steps of roasting the source in a reducing atmosphere with or without additives at a temperature in the range of from about 550.degree. to about 900.degree. C., cooling the roasted material and extracting the same with a basic leaching agent, and recovering the desired metal value, the improvement which comprises utilizing ammoniacal ammonium chloride as said basic leaching agent.
A specific embodiment of this invention is found in a hydrometallurical process for the recovery of nickel from a lateritic ore which comprises pretreating at least a portion of said ore with a mixture of hydrochloric acid and sulfur compound, roasting the treated ore in a reducing atmosphere at a temperature in the range of from about 550.degree. to about 900.degree. C., cooling the roasted ore, extracting the cooled ore with an ammoniacal ammonium chloride solution to provide a solution containing dissolved nickel metal values and recovering the desired nickel metal values.